it's the gasket or gaskets between turbo and manifold.
happens if the bolts holding the turbo to the manifold come loose or off in my case.
I had one go missing and that corner started leaking and burnt through the gasket.
when you start accelerating, it is a whirr, then as boost goes up, so does the scream and pitch.
I didn't lose any boost or power at first but eventaully I could feel that it was slugish.
if you don't replace the gasket/s, it will eventually leak at idle and you will get like a chuff chuff sound sort of like a lawn mower at idle.
nissan turbo to manifold gaskets are not that expensive.. if I remember, on my r32 gtst, it was $27 from GCG turbo's in sydney.
that pack contained the gaskets between turbo and manifold and some smaller ones for the oil and water lines.